Variable gain amplifier controller

1. An apparatus adapted to be responsive to a signal derived by a transducer, the signal having random fluctuations in amplitude due to anomalies in energy coupled to the transducer, the apparatus comprising: circuitry including: a signal input adapted to be responsive to the signal, a variable gain amplifier connected to be responsive to the signal input, and a signal output connected to be responsive to the variable gain amplifier, first and second circuits connected to be responsive to the signal output of the circuitry for respectively deriving first and second feedback signals for controlling the gain of the amplifier, the first circuit including an analog gain control circuit, the second circuit being arranged for causing the second feedback signal to have a series of constant values, each determined by the signal at the signal output of the circuitry during different successive time intervals, the first and second circuits and the variable gain amplifier being arranged so the first and second feedback signals can simultaneously affect the gain of the amplifier.

2. The apparatus of claim 1 wherein the first circuit is arranged for causing the first feedback signal to have an effect on the gain of the amplifier only in response to the signal at the signal output of the circuitry exceeding a threshold.

3. The apparatus of claim 2 wherein the first and second circuits and the variable gain amplifier are arranged for causing relative changes in the amounts that the first and second feedback signals can simultaneously affect the gain of the variable gain amplifier while the circuitry is deriving the signal at the signal output.

4. The apparatus of claim 3 wherein the second circuit includes an analog to digital converter connected to be responsive to the signal at the signal output of the circuitry.

5. The apparatus of claim 4 wherein the second circuit is arranged to derive the series of constant values by comparing an indication of the signal at the signal output of the circuitry with a reference over plural successive periods.

6. The apparatus of claim 5 wherein the circuitry includes a low pass filter connected to be responsive to the variable gain amplifier and for supplying the signal to the signal output of the circuitry.

7. The apparatus of claim 6 in combination with the transducer, the transducer comprising a head for a magnetic medium.

8. The combination of claim 7 wherein the transducer comprises a head for reading a magnetic tape medium.

9. The apparatus of claim 1 wherein the first and second circuits and the variable gain amplifier are arranged for causing relative changes in the amounts that the first and second feedback signals can simultaneously affect the gain of the variable gain amplifier while the circuitry is deriving the signal at the signal output.

10. The apparatus of claim 1 wherein the second circuit includes an analog to digital converter connected to be responsive to the signal at the signal output of the circuitry.

11. The apparatus of claim 1 wherein the second circuit is arranged to derive the series of constant values by comparing an indication of the signal at the signal output of the circuitry with a reference over plural successive periods.

12. The apparatus of claim 1 wherein the circuitry includes a low pass filter connected to be responsive to the wearable gain amplifier and for supplying the signal to the signal output of the circuitry.

13. The apparatus of claim 1 in combination with the transducer, the transducer comprising a head for a magnetic medium.

14. The combination of claim 13 wherein the transducer comprises a head for reading a magnetic tape medium.

15. An apparatus adapted to be responsive to a signal derived by a transducer, the signal having random fluctuations in amplitude due to anomalies in energy coupled to the transducer, the apparatus comprising: circuitry including: a signal input adapted to be responsive to the signal, a variable gain amplifier connected to be responsive to the signal input, and a signal output connected to be responsive to the variable gain amplifier, first and second circuits connected to be responsive to the signal output of the circuitry for respectively deriving first and second feedback signals for controlling the gain of the amplifier, the first and second circuits and the variable gain amplifier being arranged so the first and second feedback signals can simultaneously affect the gain of the amplifier, the first and second circuits and the variable gain amplifier being arranged for causing relative changes in the amounts that the first and second feedback signals can simultaneously affect the gain of the variable gain amplifier while the circuitry is deriving the signal at the signal output.

16. The apparatus of claim 15 wherein the first circuit is arranged for causing the first feedback signal to have an effect on the gain of the amplifier only in response to the signal at the signal output of the circuitry exceeding a threshold.

17. The apparatus of claim 16 wherein the first circuit includes an analog gain control circuit.

18. The apparatus of claim 15 wherein the second circuit includes an analog to digital converter connected to be responsive to the signal at the signal output of the circuitry.

19. The apparatus of claim 18 wherein the second circuit is arranged to derive a series of successive constant values by comparing an indication of the signal at the signal output of the circuitry with a reference over plural successive periods.

20. The apparatus of claim 15 wherein the circuitry includes a low pass filter connected to be responsive to the wearable gain amplifier and for supplying the signal to the signal output of the circuitry.

21. The apparatus of claim 15 in combination with the transducer, the transducer comprising a head for a magnetic medium.

22. The combination of claim 21 wherein the transducer comprises a head for reading a magnetic tape medium.

23. An apparatus adapted to be responsive to a signal derived by a transducer, the signal having random fluctuations in amplitude due to anomalies in energy coupled to the transducer, the apparatus comprising: circuitry including: a signal input adapted to be responsive to the signal, a variable gain amplifier connected to be responsive to the signal input, and a signal output connected to be responsive to the variable gain amplifier, first and second circuits connected to be responsive to the signal output of the circuitry for respectively deriving first and second feedback signals for controlling the gain of the amplifier, the first and second circuits and the variable gain amplifier being arranged so the first and second feedback signals can simultaneously affect the gain of the amplifier, the first circuit including an analog gain control circuit, the second circuit including an analog to digital converter.

24. The apparatus of claim 23 wherein the first circuit is arranged for causing the first feedback signal to have an effect on the gain of the amplifier only in response to the signal at the signal output of the circuitry exceeding a threshold.

25. The apparatus of claim 23 wherein the second circuit is arranged for causing the second feedback signal to have a series of constant values, each determined by the signal at the signal output of the circuitry during different successive time intervals.

26. The apparatus of claim 25 wherein the second circuit is arranged to derive a series of successive constant values by comparing an indication of the signal at the signal output of the circuitry with a reference over plural successive periods.

27. The apparatus of claim 23 the first and second circuits and the variable gain amplifier are arranged for causing relative changes in the amounts that the first and second feedback signals can simultaneously affect the gain of the variable gain amplifier while the circuitry is deriving the signal at the signal output.

28. The apparatus of claim 23 wherein the circuitry includes a low pass filter connected to be responsive to the variable gain amplifier and for supplying the signal to the signal output of the circuitry.

29. The apparatus of claim 23 in combination with the transducer, the transducer comprising a head for a magnetic medium.

30. The combination of claim 29 wherein the transducer comprises a head for reading a magnetic tape medium.

31. An apparatus adapted to be responsive to a signal derived by a transducer, the apparatus comprising a variable gain amplifier arrangement having an input terminal connected to be responsive to the signal and an output terminal, an analog gain control circuit having an input connected to be responsive to an output signal at the output terminal, an analog to digital converter having an input connected to be responsive to the output signal at the output terminal, and circuitry connected to be responsive to an output signal of the analog gain control circuit and an output signal of the analog to digital converter for causing the gain of the variable gain amplifier to be simultaneously controlled in response to gain control output signals resulting from the output signals of the analog gain control circuit and the analog to digital converter, the circuitry being arranged for causing both of the gain control output signals to be derived in response to the same instantaneous value of the output signal at the output terminal of the variable gain amplifier arrangement.

32. The apparatus of claim 31 wherein the variable gain amplifier arrangement includes a low pass filter for deriving an output signal adapted to be coupled to the output terminal of the variable gain amplifier arrangement.

33. The apparatus of claim 31 wherein the analog gain control circuit is arranged to have an effect on the gain of the amplifier only in response to the output signal at the output terminal exceeding a threshold.

34. The apparatus of claim 31 wherein the circuitry for causing the gain of the amplifier to be controlled is arranged for causing the gain control signal associated with the analog to digital converter to have a series of constant values, each determined by the signal at the output terminal of the variable gain amplifier during different successive time intervals.

35. The apparatus of claim 34 wherein the circuitry for causing the gain of the amplifier to be controlled is arranged for causing successive outputs of the analog to digital converter associated with several different samples the converter takes of the output signal of the variable gain amplifier arrangement to result in a constant amplitude signal for a time period associated with the duration of the samples, and the circuitry for causing the gain of the amplifier to be controlled includes a comparator for comparing the constant amplitude signal with a reference, the comparator being arranged to derive the series of constant values.

36. The apparatus of claim 31 wherein the circuitry for causing the gain of the amplifier to be controlled is arranged for causing relative changes in the amplitudes of the gain control signals that are adapted to be derived by the analog gain control circuit and the analog to digital converter while the analog gain control circuit and the analog to digital converter are responsive to the same instantaneous value of the output signal at the output terminal of the variable gain amplifier arrangement.

37. An apparatus adapted to be responsive to a signal derived by a magnetic medium transducer, the apparatus comprising: circuitry including: a signal input adapted to be responsive to the signal, a variable gain amplifier connected to be responsive to the signal input, and a signal output connected to be responsive to the variable gain amplifier, first and second circuits connected to be responsive to the signal output of the circuitry for respectively deriving first and second feedback signals for controlling the gain of the amplifier, the first and second circuits and the variable gain amplifier being arranged so the first and second feedback signals can simultaneously affect the gain of the amplifier.

38. The apparatus of claim 37 in combination with the transducer.

39. The apparatus of claim 38 wherein the transducer is for transducing magnetic flux variations of a magnetic tape.

40. An apparatus adapted to be responsive to a signal derived by a magnetic medium transducer, the apparatus comprising: circuitry including: a signal input adapted to be responsive to the signal, a variable gain amplifier connected to be responsive to the signal input, and a signal output connected to be responsive to the variable gain amplifier, first and second circuits connected to be responsive to the signal output of the circuitry for respectively deriving first and second feedback signals for controlling the gain of the amplifier, the first and second circuits and the variable gain amplifier being arranged for causing both of the first and second feedback signals to be derived in response to the same instantaneous value of the output signal at the output terminal of the variable gain amplifier arrangement.

41. The apparatus claim 40 in combination with the transducer.

42. The apparatus of claim 41 wherein the transducer is for transducing magnetic flux variations of a magnetic tape.